1. Field of the Invention
Embodiments of the present invention relate to a drive unit, an image forming apparatus such as a copier, facsimile machine, printer and so forth, incorporating the drive unit therein, peripherals disposed to the image forming apparatus and incorporating the drive unit therein, and a control method for the drive unit.
2. Description of the Related Art
Related-art image forming apparatuses have employed a stepping motor as a drive source that enables accurate position control, speed control, and hold control using pulse signals required by many parts of the image forming apparatus, such as a registration portion, a sheet conveyance portion, and an image reading portion.
The stepping motor is advantageous in that the position control, speed control, and hold control can be performed using pulse signals. However, since an excessive amount of torque needs to be applied due to the possibility of occurrence of misstep due to load fluctuation and speed change, energy efficiency can deteriorate and a bigger motor that can output power beyond the actual load may be required, and therefore it is inevitable that the motor becomes large and heavy.
By contrast, a direct current (DC) motor is highly efficient because the DC motor runs on direct current according to load amount. On the other hand, however, a single DC motor cannot achieve the accurate position control and hold control of a stepping motor.
Nevertheless, Japanese Patent No. 3503429 (JP-3503429-B) discloses a technique for controlling DC motors that provides a motor control unit that includes a pulse width modulator that outputs pulse signals including a predetermined duty, a DC motor to rotate in a predetermined direction via a bridge circuit based on the pulse signals output from the pulse width modulator, and a control unit to detect whether or not the DC motor is rotating and in which direction the DC motor is rotating based on the output from an encoder. Based on the detection results, the motor control unit adjusts the duty of the pulse signals in the pulse width modulator for the purpose of maintaining a stop of rotation of the DC motor, using the DC motor to perform position control, speed control, and hold control.
However, the technique disclosed in JP-3503429-B cannot make the DC as responsive as a stepping motor at acceleration and deceleration, and does not take the durability of the motor into account.